In the beginning I made it quite clear that this was on open-ish, sandbox style, setting with some higher leveled areas. There's no meta-game penalty for leaving and going back for reinforcements or for taking the time to do research, planning, or set up. Plus the piety system and my rolling where the players can see the dice make it pretty obvious that I'm not intentionally going for character deaths.

Our ages range from 20s to 40s and the players are really aware that most deaths have occured due to lack of preparation and dumb stunts. So we are a pretty mature bunch. Plus we've all known each other for years and years so there is quite a deep trust in this group.